In order to obtain an ultrasonic image of superficial tissue easily and quickly, a broad visual field in the vicinity of the body surface must be obtained using an array type element, or a single element, and a mechanical scanning process that must also be performed along the shape of the body surface, in a direction perpendicular to the scanning direction of the array type element or the single element. A hand-held ultrasonic probe is of great value in reducing expenditures; three-dimensional images of all superficial tissues can be obtained using a single three-dimensional ultrasonic probe, and thus, during a diagnosis, no labor is required for the exchange of probes, and a plurality of three-dimensional ultrasonic probes is not needed. However, for the acquisition of three-dimensional images of the carotid artery and the thyroid, the shape formed for the ultrasonic probe must be as small as possible, because the diagnostic locations where these organs lie immediately below the jaw. Thus, there are conflicting requests, i.e., for increasing the three-dimensional diagnosis area and for downsizing a three-dimensional ultrasonic probe. In addition, since an ultrasonic probe is hand-held, a further request is that the probe be compact and light.
A conventional superficial tissue imaging acquisition method of this type is available, whereby an ultrasonic probe is rotated while a breast applicator is interposed between a breast and the probe, and a tomogram of the overall area of the breast is obtained (see, for example, patent document 1 below).
Further, another method is one whereby an ultrasonic probe is arranged in a water tank and is swept in parallel to obtain a tomogram of an entire breast (see, for example, patent document 2 below). In addition, there is a method whereby an ultrasonic probe is swept in parallel using a belt to obtain an ultrasonic image (see, for example, patent document 3 below).
A further method is one according to which a hand-held, three-dimensional ultrasonic probe is provided by rotating the electronic scanning end of an array type element (see, for example, patent document 4 below).
According to one more method, a hand-held three-dimensional ultrasonic probe for obtaining a three-dimensional, ultrasonic image is provided by mechanically oscillating a convex-shaped array type element (see, for example, patent document 5 below).
On the other hand, when an ultrasonic image for the heart, etc., is to be obtained by scanning the body surface, ultrasonic beams must be transmitted and received through a narrow area between the ribs, because of a need to avoid a lack of an ultrasonic image for the heart, which is located beneath the ribs, due to a reflection from the ribs, etc., that are located near the body surface and have a large acoustic impedance. Further, in order to acquire such a narrow ultrasonic transmission/reception area nearer the body surface, the oscillating center of an ultrasonic element must be positioned in the vicinity of the body surface, or in an area near the surface of the body.
However, according to a hand-held, mechanical scanning ultrasonic probe that performs scanning by mechanically oscillating an ultrasonic element, since it is impossible for the oscillating ultrasonic element to directly contact an organism, an acoustic coupling liquid must be sealed by a window and a probe case, and the ultrasonic element must be oscillated or rotated inside the liquid to perform scanning. For this type of ultrasonic element, the image resolution can be increased by reducing the size of an ultrasonic beam. However, the aperture for the ultrasonic element must be optimized, and based on the element size, during oscillation, adequate clearance between the element and the window must be provided. Therefore, it is difficult for an ultrasonic transmission/reception area near the surface of an organism to be reduced, or for the oscillating center of the ultrasonic element to be located either in the vicinity of the body surface or at a location near the body surface.
There is a conventional, mechanical scanning sector ultrasonic probe of this type that includes scanning means, for converting the rotation of a motor into the oscillation of a supporting member, and that for this purpose employs parallel grooves formed in the rear face of a support member pivotally attached to a shaft provided for a roller and an arm that are fixed to a rotor, and for oscillating an acoustic element, secured to the support member, by mechanically oscillating the element (see, for example, patent document 6 below).
Furthermore, there is an arrangement that employs the mechanism described in patent document 6 with an acoustic coupling liquid, in which the acoustic velocity is slower than that of the organism, so as to establish a substantially proportional relationship between the motor rotation angle and the oscillation angle of the acoustic element (see, for example, patent document 7).
There is in addition an arrangement wherein, using an arced guide rail and a belt, an ultrasonic beam is emitted between ribs, at the virtual oscillation center located in the vicinity of the body surface (see, for example, patent document 8 below).
Patent Document 1: Japanese Utility Model Application Publication After Examination No. S59-190208
Patent Document 2: Japanese Utility Model Application Publication After Examination No. S59-111110
Patent Document 3: Japanese Patent Application Publication No. S61-13942
Patent Document 4: Japanese Patent Application Publication No. H4-282136
Patent Document 5: Japanese Patent Application Publication No. H 3-184532
Patent Document 6: Japanese Utility Model Application Publication No. S59-42970
Patent Document 7: Japanese Patent Application Publication No. H7-24659
Patent Document 8: Japanese Patent Application Publication No. H6-38962
However, the apparatus described in the invention presented in patent document 1, for dedicated mammary gland diagnoses, that rotates a conventional array-type ultrasonic probe to obtain images, and is not operated while a doctor actually holds its probe like a hand-held ultrasonic probe. Furthermore, this apparatus is also not one with which a three-dimensional ultrasonic probe can be employed for diagnosing an additional area, such as the carotid artery or the thyroid.
The invention described in patent document 2, as well as the one in patent document 1, is not related to a hand-held, three-dimensional ultrasonic probe, and the equipment described is large scale and requires additional labor, such as advance preparation. Thus, diagnosis of an additional area, such as the carotid artery or the thyroid, can not be easily performed.
Further, it can be considered possible for a mechanism that uses a belt, etc., to sweep an ultrasonic element in parallel to be applied for a hand-held ultrasonic probe by employing the invention described in patent document 3. However, in a case wherein an array type element is to be swept in parallel, using, for example, a wire or a timing belt, pulleys must be arranged at either end of the element to be swept. In a case wherein structure is employed, the shape size of the organism contact portion is always larger than the mechanical sweeping range because of the width of the element and the diameters of the pulleys. Thus, this arrangement is not preferable for a hand-held three-dimensional ultrasonic probe. And especially in a case for performing a diagnosis for the carotid artery or the thyroid, a problem is that a hand-held three-dimensional ultrasonic probe can not contact a desired location for a target portion of an organism because a jaw, etc., obstructs the location.
Moreover, the invention described in patent document 4 relates to the acquisition of a three-dimensional ultrasonic image by rotation performed at the electronic scanning end of an array type element, and compared with a mechanical rotational movement near the center, rotational movement at a location separated from the rotation center is increased. Therefore, the pitch of the two-dimensional plane, which is the original data used for constructing a three-dimensional image, becomes smaller nearer the rotation center, while the pitch becomes larger as the distance from the rotation center increases. Thus, in proportion to the distance from the rotation center, the pitch of two-dimensional slices is increased, and when a three-dimensional image is formed based on image data for a position separated from the rotation center, a problem is that the resolution for the portion separated from the rotation center is lower.
Further, when rotation is performed at the electronic scanning end of an array type element, a mechanism is required for which a rotation axis is located at a position extended from the length of the array element in the electronic scanning direction. Thus, in a case wherein a diagnosis for a portion such as the carotid artery or the thyroid is to be performed, a problem is that an organism contact portion longer than the element may strike the jaw portion, making it difficult for an ultrasonic probe to contact a desired location.
Further, according to the three-dimensional ultrasonic probe presented in patent document 5 described above, since a three-dimensional image is obtained by mechanical oscillation of the convex-shaped array type element, the curvature of the organism contact portion at the tip of the probe is determined depending on the distance between the oscillation center of the element and the tip of the array type element. Therefore, when the organism contact portion is shaped so that, using mechanical scanning, the two ends there are appropriately brought into contact with a comparatively flat, superficial tissue portion of an organism, a large distance is required from the mechanical oscillation center to the tip of the array type element, and the curvature of the organism contact portion must be increased. In addition, when the distance from the mechanical oscillation center to the tip of the array type element is extended, the size of a hand-held, three-dimensional ultrasonic probe is increased, and this presents a problem in that the increase in the size and the weight of the hand-held three-dimensional ultrasonic probe make handling the probe difficult when performing a diagnosis.
Further, the invention described in patent document 6 provides a mechanism, which converts the rotational movement of the motor into the oscillation of the support member, by using parallel grooves, which are formed in the rear face of the support member, pivotally attached to the shaft provided for the roller and the arm that are secured to the rotor, and which oscillates an acoustic element secured to the support member to oscillate the element mechanically. Therefore, a problem encountered is that the oscillation angle of the element is not proportional to the rotational angle of the motor, and in a case wherein the velocity at which the motor rotates is a constant, the ultrasonic beam can not be oscillated at the same angle.
Furthermore, since sequentially the motor is rotated in one direction and the above described mechanism converts the rotational movement into oscillation, the oscillation angle of the element, i.e., the acoustic scanning angle, becomes a constant. And in a case wherein an organ, such as the heart, which provides rapid movement, is employed as an ultrasonic diagnosis object, when the motor is rotated fast, so that movement of the organ can be tracked well, for drawing an ultrasonic image, the density of acoustic scan lines may be reduced and image deterioration may occur. A period during which the organism depends on the acoustic velocity is required in order to obtain an ultrasonic echo from the organism, and oscillation at a small scanning angle is required in order to obtain an ultrasonic image of a rapidly moving organ, without deterioration of the image. However, according to the invention described in patent document 6, it is difficult for the oscillation velocity to be increased by setting an arbitrary oscillation angle. Furthermore, since an inverse proportion is established between the scanning line density and the angular oscillation velocity, a problem is that, for the above described mechanism, the angular oscillation velocity is high in the middle of the oscillation angle that is especially important, i.e., the scanning line density is lowered.
In addition, according to the invention described in patent document 6, oscillation is performed at the oscillation axis of the element that is located inside the window that contacts the organism. Because of this structure, the oscillation center of the element has to be located separate from the window that contacts the organism, i.e., separate from the organism, so that the actual acoustic scan lines are spread on the surface of the window, i.e., on the organism contact portion. Thus, a problem is that, when an organ, such as the ribs, that has a large acoustic impedance and that greatly reflects an ultrasonic beam, is present near the organism, an ultrasonic beam is interrupted by the organ, such as the ribs, and can not reach the organ present below, inside the organism.
Moreover, according to the invention described in patent document 7, the mechanism described in patent document 6 is employed with an acoustic coupling liquid, for which the acoustic velocity is slower than that for the organism; however, a complete proportional relation is not established between the motor rotational angle and the oscillation angle of the acoustic element. Furthermore, according to the invention described in patent document 7, as well as that in patent document 6, the oscillation is performed at the oscillation axis of the element that is located inside the window that contacts the organism. Because of this structure, the oscillation center of the element must be located separate from the window that contacts the organism, so that the actual acoustic scan lines are spread on the surface of the window, i.e., on the organism contact portion. Thus, there is a problem in that, when an organ, such as a rib, that has a large acoustic impedance and that greatly reflects an ultrasonic beam, is present near the organism, an ultrasonic beam will be interrupted by the organ, such as the rib, and can not reach an organ located below, inside the organism. In addition, as in patent document 6, since it is difficult to provide an improvement for time-transient tracking relative to an organ that moves rapidly, the oscillation velocity is increased by reducing the oscillation angle, and it is also difficult for the scanning line density and the oscillation velocity to be arbitrarily set in consonance with a diagnosis portion.
Moreover, according to the invention described in patent document 8, since there is a limitation on the width of the arm, which is fitted to and slides along the guide rail, and for the interference of the roller provided outside the guide rail, the roller must be arranged outside the actual element oscillation range, and the outer shape of the probe must be extended in accordance with the location of the roller. Therefore, this is a problem related to a reduction in the size and the weight of the probe. Further, when an organ, such as the heart, is to be scanned along the lower edge of the costal arch, i.e., from below the ribs, the probe must be moved from below the ribs to substantially parallel to the body surface, and the roundness of the probe due to the presence of the roller interferes with the scanning operation. In addition, since multiple parts, such as a guide rail, a plurality of rollers and a belt, are required for the mechanism, the total cost for these parts and the complicated assembly process are also problems.